1. Field of the Invention
This invention relates to a polarization independent optical isolator.
2. Description of the Prior Art
A polarization independent optical isolator in, for example, Japanese Patent Application Public Disclosure No. SHO 54-14709, published Nov. 16, 1979. This conventional optical isolator comprises first, second and third birefringent crystals having flat plate shapes and first and second rotators providing 45.degree. of Faraday rotation and interposed between the first and second birefringent crystals.
The first, second and third birefringent crystals of the aforenoted conventional optical isolator have thickness ratios of .sqroot.2:1:1. That is to say, the processing for preparing the birefringent crystals of two sorts different in thickness (one relatively thick birefringent crystal and two relatively thin birefringent crystals) consumes labor and proves to be troublesome. Thus, the conventional optical isolator has suffered a disadvantage such that it is unsuitable for mass production.